sinoatrial (SA) node

Atrial tachycardia and other ectopic atrial rhythms occur when a site outside of the sinus node, but within the atria, creates action potentials faster than the sinus node. If less than 100 beats per minute, then the term “ectopic atrial rhythm” is used.

SA node

What is atrial fibrillation? Atrial fibrillation (AF or AFib) is the most common irregular heart rhythm that starts in the atria. Instead of the SA node (sinus node) directing the electrical rhythm, many different impulses rapidly fire at once, causing a very fast, chaotic rhythm in the atria.

The basic pattern of the ECG is logical: electrical activity towards a lead causes an upward deflection. electrical activity away from a lead causes a downward deflection. depolarization and repolarization deflections occur in opposite directions.

An ECG Can Recognize the Signs of Blocked Arteries. Unfortunately, the accuracy of diagnosing blocked arteries further from the heart when using an ECG decrease, so your cardiologist may recommend an ultrasound, which is a non-invasive test, like a carotid ultrasound, to check for blockages in the extremities or neck.

Compressional waves are also called P-Waves, (P stands for “primary”) because they are always the first to arrive. Shear waves propagate more slowly through the Earth than compressional waves and arrive second, hence their name S- or secondary waves.

Absence of P Waves A lack of visible P waves preceding QRS complexes suggests a lack of sinus beats; this may occur with sinus dysfunction or in the presence of fibrillation or flutter waves. The P wave may also be hidden within the QRS complex.

P-waves travel 60% faster than S-waves on average because the interior of the Earth does not react the same way to both of them. P-waves are compression waves that apply a force in the direction of propagation. The energy is thus less easily transmitted through the medium, and S-waves are slower.

Even in large earthquakes the intense shaking generally lasts only a few tens of seconds, but it can last for minutes in the greatest earthquakes. At farther distances the amplitude of the seismic waves decreases as the energy released by the earthquake spreads throughout a larger volume of Earth.

mantle

These waves can travel through solids, liquids, and gases. P waves can travel through the liquid outer core. An S wave is a different beast. In an S wave, the rock particles slide past one another, undergoing shear — so an S wave is also called a shear wave.

Answer Expert Verified P-waves of primary waves originate from the epicenter. Since each city has a different distance from the epicenter, the p-waves will arrive at different times.

The epicenter is the point on the earth’s surface vertically above the hypocenter (or focus), point in the crust where a seismic rupture begins.

What happens to the times difference between primary and secondary waves as the distance traveled gets longer? The time differences become bigger. Suppose a primary and secondary wave both travel a distance of 4,000 km before they are picked up by a seismograph.

By locating the place on the seismogram (Fig. 2) where the P wave begins (in this case at time ‘0’) then locating the time when the S wave arrives (in this case 64 seconds) you can determine the time lag between the arrival of the P wave and the arrival of the S wave (S – P = Lag, 64 – 0 = 64 sec).

The P wave will be the first wiggle that is bigger than the rest of the little ones (the microseisms). Because P waves are the fastest seismic waves, they will usually be the first ones that your seismograph records. The next set of seismic waves on your seismogram will be the S waves.

S waves are slower than P waves by a known amount. Therefore, the farther a seismic recording station is from the earthquake epicenter the greater will be the difference in time of arrival between the P and S wave.